From cf7248d004153194ce15a215afc0803e9798ecb7 Mon Sep 17 00:00:00 2001
From: "Dmitry V. Levin" <ldv@altlinux.org>
Date: Sun, 11 Jan 2015 17:26:29 +0000
Subject: [PATCH] arm: rewrite shuffle_scno in a bit more readable way

* linux/arm/syscallent.h: Define ARM_FIRST_SHUFFLED_SYSCALL instead of
ARM_LAST_ORDINARY_SYSCALL.
* syscall.c [ARM || AARCH64] (shuffle_scno): Update.
---
 linux/arm/syscallent.h |  6 +++---
 syscall.c              | 33 +++++++++++++++++----------------
 2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/linux/arm/syscallent.h b/linux/arm/syscallent.h
index 5bde8bd9..c93eaa4c 100644
--- a/linux/arm/syscallent.h
+++ b/linux/arm/syscallent.h
@@ -412,7 +412,7 @@
 	{ 4,	0,	sys_sched_getattr,	"sched_getattr"	}, /* 381 */
 	{ 5,	TD|TF,	sys_renameat2,		"renameat2"	}, /* 382 */
 #ifdef __ARM_EABI__
-# define ARM_LAST_ORDINARY_SYSCALL 382
+# define ARM_FIRST_SHUFFLED_SYSCALL 383
 #else
 	{ 5,	0,	NULL,			NULL		}, /* 383 */
 	{ 5,	0,	NULL,			NULL		}, /* 384 */
@@ -433,8 +433,8 @@
 	{ 5,	0,	NULL,			NULL		}, /* 399 */
 # define SYS_socket_subcall	400
 # include "subcall.h"
-# define ARM_LAST_ORDINARY_SYSCALL (SYS_socket_subcall + SYS_socket_nsubcalls + SYS_ipc_nsubcalls - 1)
-#endif /* !EABI */
+# define ARM_FIRST_SHUFFLED_SYSCALL (SYS_socket_subcall + SYS_socket_nsubcalls + SYS_ipc_nsubcalls)
+#endif /* !__ARM_EABI__ */
 
 	/* __ARM_NR_cmpxchg (0x000ffff0).
 	 * Remapped by shuffle_scno() to be directly after ordinary syscalls
diff --git a/syscall.c b/syscall.c
index 091626ce..343fa308 100644
--- a/syscall.c
+++ b/syscall.c
@@ -930,34 +930,35 @@ print_pc(struct tcb *tcp)
 #endif /* architecture */
 }
 
-/* Shuffle syscall numbers so that we don't have huge gaps in syscall table.
- * The shuffling should be reversible: shuffle_scno(shuffle_scno(n)) == n.
+/*
+ * Shuffle syscall numbers so that we don't have huge gaps in syscall table.
+ * The shuffling should be an involution: shuffle_scno(shuffle_scno(n)) == n.
  */
 #if defined(ARM) || defined(AARCH64) /* So far only 32-bit ARM needs this */
 static long
 shuffle_scno(unsigned long scno)
 {
-	if (scno <= ARM_LAST_ORDINARY_SYSCALL)
+	if (scno < ARM_FIRST_SHUFFLED_SYSCALL)
 		return scno;
 
 	/* __ARM_NR_cmpxchg? Swap with LAST_ORDINARY+1 */
-	if (scno == 0x000ffff0)
-		return ARM_LAST_ORDINARY_SYSCALL+1;
-	if (scno == ARM_LAST_ORDINARY_SYSCALL+1)
+	if (scno == ARM_FIRST_SHUFFLED_SYSCALL)
 		return 0x000ffff0;
+	if (scno == 0x000ffff0)
+		return ARM_FIRST_SHUFFLED_SYSCALL;
 
-	/* Is it ARM specific syscall?
-	 * Swap with [LAST_ORDINARY+2, LAST_ORDINARY+2 + LAST_SPECIAL] range.
+#define ARM_SECOND_SHUFFLED_SYSCALL (ARM_FIRST_SHUFFLED_SYSCALL + 1)
+	/*
+	 * Is it ARM specific syscall?
+	 * Swap [0x000f0000, 0x000f0000 + LAST_SPECIAL] range
+	 * with [SECOND_SHUFFLED, SECOND_SHUFFLED + LAST_SPECIAL] range.
 	 */
-	if (scno >= 0x000f0000
-	 && scno <= 0x000f0000 + ARM_LAST_SPECIAL_SYSCALL
-	) {
-		return scno - 0x000f0000 + (ARM_LAST_ORDINARY_SYSCALL+2);
+	if (scno >= 0x000f0000 &&
+	    scno <= 0x000f0000 + ARM_LAST_SPECIAL_SYSCALL) {
+		return scno - 0x000f0000 + ARM_SECOND_SHUFFLED_SYSCALL;
 	}
-	if (/* scno >= ARM_LAST_ORDINARY_SYSCALL+2 - always true */ 1
-	 && scno <= (ARM_LAST_ORDINARY_SYSCALL+2) + ARM_LAST_SPECIAL_SYSCALL
-	) {
-		return scno + 0x000f0000 - (ARM_LAST_ORDINARY_SYSCALL+2);
+	if (scno <= ARM_SECOND_SHUFFLED_SYSCALL + ARM_LAST_SPECIAL_SYSCALL) {
+		return scno + 0x000f0000 - ARM_SECOND_SHUFFLED_SYSCALL;
 	}
 
 	return scno;
-- 
2.40.0